1. Field of the Invention
The invention relates more in particular to such a method and apparatus wherein non-cohesive bottom material, such as for example sand, or soft clay of mixtures of sand and soft clay, is fluidized by injecting a fluid at low velocity and at low pressure into the bottom material and wherein the conduit is allowed to sink into the fluidized bottom material.
2. Prior Art
A related method and apparatus is described in British Pat. Nos. 1,219,879 and 1,291,250. The method of these patents is satisfactory when applied to the burying of a conduit in a bottom of a body of water when the bottom material along the planned route of the conduit is non-cohesive. However, when in certain areas of the planned route of the conduit lumps of cohesive material, for example lumps of hard clay, are present, difficulties may arise when the method of the above kind is applied. This is caused by the fact that the fluid used for the fluidization of the non-cohesive bottom material is injected at low pressure and at low velocity so that the fluid is not able to erode lumps of cohesive bottom material such as hard clay.
In order to erode the lumps of cohesive bottom material high pressure fluid jets can be used, for example having a nozzle pressure drop in the range of about 100 to 1,000 psi.
Power consumption of such high pressure jets is, however, rather high, in particular since a large number of such high pressure jets have to be applied because in cohesive bottom material such as hard clay, each jet issuing from a high pressure nozzle creates a hole having only a small diameter.
Other pertinent art includes U.S. Pat. Nos. 2,659,211; 3,181,301; 3,504,504; 3,638,439; 3,751,927; 3,786,642; 3,877,237.